Labour MPs were yesterday shell-shocked - not so much by the size of their defeat, but that they had got so far out of touch with middle New Zealand that John Key's party could waltz back into power more popular than ever before, and with an unheard of outright majority.

The anger from the likes of former leader David Shearer was palpable - and visceral.

Others were also lining up to publicly attack Labour's strategy and direction and acknowledge that they had lost their way.

Leader David Cunliffe's demeanour will fuel their rage.

Cunliffe found many factors to blame for Labour's defeat - the economy, being starved of oxygen by dirty politics, the Dotcom bomb and secret surveillance, and the party's utter failure to fundraise.

But the one finger he did not point was at himself.

He declared repeatedly that he had the energy and vision to lead Labour into the future.

And he repeatedly referred to his support from the wider membership - a coded message to his caucus that even if they don't back him, under Labour's constitution he does not need them.

Just as happened with the leadership vote that installed him over the wishes of a majority of MPs, Cunliffe can be re-elected leader so long as he retains the loyalty of the unions and the grassroots.

That rule was imposed on the caucus by an activist base from which the MPs have grown increasingly estranged as party conferences increasingly turn into bitter fights over issues such as female quotas.

The anti-Cunliffe faction will look to Saturday night's result as a lesson to the grassroots that the MPs were right about what's important to middle New Zealand, and the activists wrong.

If Cunliffe wins the leadership primary - and Saturday's rout will make that harder - loyalists will likely press for a purge.

That will only prolong the disunity and instability that led to Saturday's defeat. If Cunliffe loses, he will only have to look back to his concession speech.

Key spent his first day back on the job after his election victory preaching the perils of arrogance and hubris to his caucus.

Similar humility from Cunliffe would have gone a long way to mending bridges with his caucus.